Two clones of 1.4 and 4.33 kilobase pairs (kbp) DNA inserts, were selected from a Sarcocystis cruzi sporozoite genomic library constructed in bacteriophage lambda gt10. These clones strongly hybridized with sporozoite and merozoite DNA and were evaluated as probes for detection of merozoite DNA in clinical samples. Of five calves in the experiment, four were each orally dosed with approximately 200,000 S. cruzi sporocysts; one calf served as non-infected control. Subsequently, blood was Show moreTwo clones of 1.4 and 4.33 kilobase pairs (kbp) DNA inserts, were selected from a Sarcocystis cruzi sporozoite genomic library constructed in bacteriophage lambda gt10. These clones strongly hybridized with sporozoite and merozoite DNA and were evaluated as probes for detection of merozoite DNA in clinical samples. Of five calves in the experiment, four were each orally dosed with approximately 200,000 S. cruzi sporocysts; one calf served as non-infected control. Subsequently, blood was collected from the calves twice weekly for 3.5 months and fractionated into buffy coats, polymorphonuclear cells, and plasma. Total cellular DNA extracted from these fractions was dot blotted on nylon membranes and hybridized with the probes radiolabeled with [alpha-32P]dATP. The probes detected merozoites on Day 22 post infection in the buffy coats and intermittently from Day 25-39 in the granulocyte fraction. Parasitemia (i.e. merozoites in blood) was also detected by indirect fluorescent antibody technique (IFAT) and direct microscopy, Diagnosis of sarcocystosis in cattle using genomic DNA probes by dot blot hybridization provides an alternative method of detecting parasitemia that is more rigorous than the other two tests (IFAT, direct microscopy) which rely on morphology of the merozoite and visualization by the examiner. As probes detected merozoite DNA in the granulocyte fraction, polymorphonuclear cells may be involved in the pathogenesis of S.cruzi; however this hypothesis requires further study. Show less